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Best wireless chargers – how they work and perform

Wireless charging is one of those technologies which should really be built into every mid-range and high-end phone, because it frees us, in part at least, from those cable bird nests we all have. However, sadly it isn’t built into many phones. The reasons why it isn’t, are many, some to do with the tech itself, some to do with costs, and some to do with the politics of competing standards.

If you have a phone that supports Qi wireless charging then you probably didn’t get a wireless charger in the box. So, what wireless charger should you buy? Does it make a difference? Are they all the same? Well let’s find out.

How does it work?

Coils of wire create magnetic fields, which can be used to generate a current flow in a separate, insulated coil. This is the basis of transformer technology.

Back in 1831 Michael Faraday discovered electromagnetic induction, where electricity is made by passing a magnet through a coil of wire. Today we use this phenomenon for a wide range of applications including transformers, electrical motors, generators, solenoids and wireless charging.

Essentially Qi wireless charging uses two coils of wire. The charging station contains one coil which produces an oscillating magnetic field, which in turn induces electricity in the receiving coil in your smartphone.

Because of the nature of electromagnetic induction and the Qi wireless standard, the charger and the phone must be very close to each other. The close nature of this connection ensures a good level of transferable power, but it does have its drawbacks, mainly that the charger and the smartphone need to be lined up fairly accurately in order to achieve a good connection.

Best chargers

Samsung Wireless Qi Charging Station

This wireless charger from Samsung is an official accessory of the Galaxy S6, and is very easy to use. This round charger has a small footprint and requires minimal space. It has a built-in LED indicator light to alert you if your device is not properly aligned and when a good charge alignment is acquired (LED lights up blue). If you are using it with the Galaxy S6, it will also alert you when your device is fully charged (LED lights up green). The charger also comes with over-charging protection. Since this is a Qi charger it is compatible with any other smartphone that comes with Qi wireless charging capabilities.

At the time of writing the Samsung Wireless Charger is available on Amazon for just $29.99, with color options including black sapphire and white pearl.

Anker Ultra-Slim Wireless Charging Pad

The Anker Ultra-Slim Wireless Charging Pad holds true to its name and is about the same size and thickness of a coffee cup coaster. Proper alignment is required, and a LED light indicates charging status. This charger also comes with a power efficient idle mode to prevent overcharging your device. Charging devices with a case on is possible, but like most other chargers, will see a reduction in performance if the case is thicker than 5 mm. The Anker Ultra-Slim Wireless Charging Pad is available for $19.99.

RAVPower Wireless Qi Charging Pad

With its anti-slip silicon pad that helps keep your phone secure in its place, this Qi compatibile wireless works with many popular Android devices including the Samsung Galaxy S6, the Galaxy S5, the Galaxy S4, the Nexus 7 (2013), the Nexus 6, the Nexus 5, and the Nexus 4. The pad also has an LED to show you when you phone is charging.

You can pickup a RAVPower Wireless Charging Pad for just $24.99 from Amazon.

How did they perform?

To test these charging pads I defined several different criteria. First, how easy is it to align and place the phone on the charger. Second, what feedback do I get that the phone is charging. Third, how quickly does the phone charge and what power is being drawn by the charger. I used a Galaxy S6 Edge for all the tests and started with the battery at zero.

So that we have some context about charging times, the Samsung Galaxy S6 Edge has a 2600mAh battery which will charge from zero to 100% in around 1 hour and 20 minutes using Samsung’s wired quick charger that comes with the phone.

Two more things to mention. First, the charging cycle for a Li-ion battery is performed in two stages. This is true for standard wired charging, for quick charging and for wireless charging. During the first stage a constant current is applied to the battery. Then when the battery is around 80% to 90% full (depending on the exact battery design) the current will be lowered but the voltage will remain the same.

The second thing is that to measure the voltage and current being used by the charger I used an inline USB volt and amp meter (pictured below). However this will only tell me the current and voltage being used by the charger itself, it can’t reveal what is happening in the coils. Since the non-fast version of Qi standard specifies a maximum power limit of 5W, we can see that at least 1W is being lost in conversion.

Samsung Wireless Qi Charging Station

The Samsung is the first of our circular pads which we are testing. Whereas the Anker wants to be “ultra-slim” the Samsung pad bring some shape and design. The lower half of the charger is smaller and it curves up to the full pad. The top of the pad is ringed by an LED strip which allows the notification light to be easily seen (more about that in a moment), and on top of the pad is a silicon circle to help keep your phone in place. Aligning the phone on the pad is easy enough, you just need to put the center of the phone on the center of the pad. You can place the phone in any orientation.

When you place the phone on the pad you get a nice reassuring blue glow from the ring around the top of the charger. If you are using a Galaxy S6 or S6 Edge (and I guess a Note 5 or S6+ Edge) then the LED goes green when the phone is charged.

Charging time was just over 2 hours and 40 minute from zero to 100%. The charger draws 6 watts of power fairly consistently until the battery reaches around 90% charge, then it starts to tail off. At the end of the charge cycle it is drawing around 2.5 watts.

Anker Ultra-Slim Wireless Charging Pad

Aligning the phone on the Anker is simple enough, you basically just need to put the center of the phone on the center of the pad. Since the pad is circular you can actually place the phone in any direction and you don’t necessarily need it to be straight up-down or horizontal. There is no rubber or silicon on the pad, so it is the most slippery of the three. Having said that, I didn’t have any trouble getting the phone to stay on the pad, however the phone might be prone to moving off-center if you dump into your desk accidentally.

The pad doesn’t come with any kind of beeper/buzzer and the only indication from the pad that you are charging the phone comes from a small LED. Unfortunately the LED can be easily obscured by your phone if you place it with the end overhanging the LED position. However, your phone should also give an indication that it is charging correctly, or alternatively it isn’t hard to form the habit of avoid certain orientations of your phone on the pad.

In terms of charging performance, the Anker performed just as well as the Samsung and the RAVPower. It charged from zero to 100% in around 2 hours and 40 minutes. The pad was using just over 6 watts of power for the first couple of hours until the battery reached around 80% and then it started to decrease, slowly at first until about 90% and then more sharply as the battery reached its full charge.

RAVPower Wireless Qi Charging Pad

Unlike the other two charging pads the RAVPower is a rectangle rather than a circle. Personally I prefer this design as it defines very clearly where the phone should be placed. However like the other pads you don’t actually need to place the phone long ways to match the pad’s design, you can actually place it at any angle, as long as the center of the phone is in the center of the pad. It is also worth mentioning the white circle around the power symbol in the middle of the pad is an anti-slip silicon, which helps minimize slipping or movement due to knocks.

As well as an LED that shows that the phone has been placed correctly on the pad, the RAVPower also has a built-in beeper which sounds when a good connection has been made. This gives you a reassurance that everything is working as expected.

The performance of the pad is very similar to that of the other two. It takes around two hours and forty minutes to charge the Samsung Galaxy S6 Edge from zero to 100%. The charger draws just over 6 watts of power for just over two hours until the battery gets close to 90% full. Then it starts to decline, eventually dipping to under 3 watts as the battery reaches its full charge.

So what does that all mean?

There are a few lessons to be learnt from these tests:

Although this might be obvious to some, it is worth pointing out: Wireless chargers take longer to charge a phone than a wired charger, especially if the wired charger has any kind of quick charge functionality. However, wireless charging is faster than plugging your phone into standard 0.5A USB 2.0 port. The Galaxy S6 takes around 6 hours to charge using a normal USB port.

The charging times are identical for each charger. This is because each charger implements the Qi standard and the Qi standard dictates how much power can be delivered and at what rate the phone is charged. It doesn’t seem that one implementation is better than another. For all I know they could be all using the same standard charging circuit and components.

Your buying decision will be based on what the pad offers other than a wireless charging circuit. Do you want silicon grips, a beeper or buzzer, or a nice glowing LED band? Do you want it round or square? Black or white? And so on.

Honorable mentions

For this test I concentrated on three particular chargers, however if these don’t fit your needs then you might also find these chargers of interest:

Wireless Charging Stand with 3 Quick Charging USB ports

Save space, save money and conveniently charge all your devices from 1 hub. Wirelessly charge your phone by placing it on the charging pad and charge up to 3 other devices with our 3 USB ports. Includes (1) QC Quick Charge 3.0 port (2) Smart USB Charging ports that will send the maximum available charge.

Buy At Amazon

Qifull Wireless Car Charging Dock

The Qifull Wireless Car Charging Dock comes with both a suction cup mount and an air vent bracket, and works in both portrait and landscape orientation. It comes with a button on the back to adjust the width of the charger holder dock. 3 transmitting coils works together to fully cover the wireless charger for full direction transmission. Built-in strong automatic protective IC gives high efficiency and safety while charging, and a LED light to shows the charging condition, with the color changing from blue to green to show when the device is fully charged. The Qifull Wireless Car Charging Dock is available for $28.99.

Wrap up

If you are in the market for a wireless charger then there are lots of products available. In terms of charging times, it doesn’t seem to matter which one you get. Does that surprise you? I must admit it did surprise me, I was expecting at least some variance! So it looks like it all comes down to aesthetics and function.

Do you use wireless charging? If so, what charger do you have? Did any of the chargers I tested peak your interest in wireless charging?

Gary has been a tech writer for over a decade and specializes in open source systems. He has a Bachelor's degree in Business Information Systems.He has many years of experience in system design and development as well as system administration, system security and networking protocols. He also knows several programming languages, as he was previously a software engineer for 10 years.